Research on Modeling of Satellite On-orbit Operation Procedure

Aiming at the demand of the TT&C system for the on-orbit satellite to automatically perform various operations, the paper proposes a modeling technology for on-orbit operation procedures. Based on the formal method, a grammer specification of operating rules is formulated, and modeling rules of operating rules are defined by XML Schema. The process of graphical editing, serialization and deserialization of operating rules is presented. Practical application shows that it can improve the design and execution efficiency of operating procedures.


1.Introduction
During the on-orbit lifecycle of satellites, it is necessary to use the TT&C system [1] to arrange the satellite operation according to certain logic and form control instructions. Through the station, instructions are injected into the satellite, and the execution effect of the instructions is interpreted, so as to complete the TT&C operation, payload operation and abnormal handling of the satellite. With the increasing number of satellites on orbit and the complexity of satellite functions, requirements for the TT&C system are increasing [2] . Efficient assignments for on-orbit operations, generalization and automatic execution of the operations, has become the core issue to be solved for the TT&C system.

2.Procedure Language Grammar
For all kinds of operations, standard and automatic procedures need to be designed. To describe the operation procedures of on-orbit satellites, we need a fully functional language [3] which covers all the atomic operations and logical structures of on-orbit operations. Through the analysis and induction of the on-orbit operation process, based on normal form rules in BNF [4] , the grammar of the operation rules if formally defined as follows.

2.5.Manual Confirm Paradigm
Suspend procedure execution and show tip for the operator to confirm. The paradigm is as follows: ASK_STATEMENT ::= "ask" "(" <TEXT> ")" Texts following the key word "ask" represent information to be confirmed by the operator.

3.Procedure Modelling, Serialization and Deserialization
Based on the formal definition of the procedure grammar, and according to demand of on-orbit operation, operation program can be designed [5] . Traditionally, satellite operators write operation program scripts directly and then compile and run the program by compiler [6] . The paper proposes a graphical modeling method for the design of operation procedures, which is more efficient and intuitive than writing scripts or tabular documents [7] [8] , and has good readability and maintainability.

3.1.Procedure Model
The paper uses XML Schema to establish the entity model of operating procedures. The model is based on the formal syntax of operating procedures, and offers an XML representation for the procedures so that the operating procedures can be saved as an XML file and loaded from the XML file to graphical interface. The XML Schema definition is shown in the following figure. The model root element is "Procedure", which represents the operating procedure. It contains 0 to multiple (minOccurs=0, maxOccurs=unbounded) sequence of "ProcedureStep" type elements.
The type "ProcedureStep" is a complex type that represents a single step in a sequence of procedures. "ProcedureStep" has attribute and sequence of child elements. The attributes of "ProcedureStep" are show in table 1. "ProcedureStep" type's sub element sequences are also "ProcedureStep" type, thus supporting multilayer nesting of procedures.

3.2.Editing, Serialization and Deserialization
Since we have an XML Schema definition for the procedures, next we can edit, store, and load the procedures through a tabulated graphical user interface. The detailed process is show in the following figure (with the Java language implementation as an example).  Fig.2 Procedure model graphical editing, serialization and deserialization 1) Through the JAXB tool, the XML Schema of the operating procedure is mapped to the Java beans of the operating procedure; 2) Make a data binding between graphical table and the Java Bean arrays of the procedure; 3) According to the requirements of on-orbit satellite operations, add new step lines and edit attributes of each step line until all the steps of the procedure finishing; 4) By using data binding, transfer the procedure in the graphical table to Java Bean arrays; 5) Through the JAXB tool, serialize the procedure's java bean arrays to an XML file, which conforms to the procedure's XML Schema constraints established in step 1; 6) With the JAXB tool, we can deserialize the XML files of procedures into Java Bean arrays. By using data binding, procedures can be displayed and edit in the graphical table editor.
By this process, we complete the formalization definition, XML Schema definition, graphical design, serialization, preservation, deserialization, loading display and other key modeling issues of on-orbit operation procedures.

4.Application Effect
Based on the above research results, the satellite on-orbit operating software can realize the design of operating procedures and automatic execution. The system has been deployed at the ground station and applied to the on-orbit operation of multiple communication satellites, realizing operations like position keeping, gyro calibration. The system interface is as follows.

5.Conclusion
The paper focuses on the description and modeling of satellite on-orbit operating procedures, and gradually conducts research from abstract to specific. Through the formalization, the XML Schema definition, graphical display and editing, saving (serialization) and loading (deserialization), we complete the operating procedure modeling process. The on-orbit operation software developed based on the research results can cover various types of on-orbit satellite operation requirements, realize the operating procedures of graphical design and persistent storage. It is easy to load, display and execute. The established operating procedures have good practicability, readability, reusability and maintainability, and have a good practical application effect on improving the management and automatic operation capability of satellite on-orbit operating procedures.